This invention relates to improvements in chemical reaction systems, and particularly to such chemical reaction systems when applied to photographic processes. The invention also relates to apparatus for use therewith.
It is often the case in chemical reaction systems that a chemically reactive substrate is presented sequentially to a number of different reaction sites in sequence. One of the problems with such serial reactions is carry-over of reactive materials as a result of a wetting action of the reactive substrate by the chemical reactants concerned. Another problem is that even if reactants from a first stage are mutually compatible with reactants in a second or subsequent stage, very often the by-products of reaction in one stage have a deleterious effect on reactions to follow. This problem becomes worse as the relative speed of the reactive substrate increases. This problem is particularly acute in the processing of photographic paper, but is of course equally applicable to serial treatment of textile webs for example where similar problems arise.
In our WO-A-8702150 there is described a multi-stage countercurrent contacting process wherein a solid is introduced sequentially to a plurality of stages and is reacted with a liquid reactant flowing in the opposed sense.
In this disclosure the depleted liquid reactant is removed from the last contacting stage for disposal or upgrading.